Dockerized-3tier-java-app

I have containerized a pre-existing Spring Boot + Thymeleaf Java application along with a MySQL database, using Docker Compose to create a reliable, reproducible multi-container environment that handles service orchestration, networking, and data persistence.

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🎯 Project Goals

• Multi-Stage Dockerfile

  1. Build stage: compile the application with Maven and OpenJDK (maven:3.8.3-openjdk-17) to produce an executable JAR.
  2. Runtime stage: start from a minimal Alpine-based OpenJDK 17 image (bellsoft/liberica-openjdk-alpine:17), copy in only the packaged JAR, and launch it—keeping the final image lean.

• Docker Compose v3.8
  Orchestrate two services—java_app (Spring Boot + Thymeleaf) and mysql_db—on an isolated bridge network, mount a named volume for persistent MySQL data, and use health checks to ensure proper startup order.

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🏗️ Architecture Overview

flowchart LR
    BROWSER["Browser (Thymeleaf UI)"]
    APP["java_app (Spring Boot)"]
    DB["mysql_db (MySQL Container)"]
    VOLUME["mysql-data (Docker Volume)"]

    BROWSER -->|HTTP| APP
    APP -->|JDBC| DB
    DB -->|Persists Data| VOLUME

    subgraph "Docker Network"
        direction LR
        APP
        DB
    end

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🚀 Setup & Installation

1. Clone the repository

   git clone https://github.com/DevDetroja10/Dockerized-3tier-java-app.git

2. Build and start all services

   docker compose up 

3. Access the application
   Open your browser and navigate to:

   http://localhost:8080
   

⚠️ Note: The application may take a few seconds to fully start after the database initializes. If you encounter a connection error, wait briefly and refresh the page.

4. Stop all services

   docker compose down

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⚙️ Configuration Variables

Variable	Description
SPRING_DATASOURCE_URL	JDBC URL for connecting to the MySQL container
SPRING_DATASOURCE_USERNAME	Database username used by the Spring Boot app
SPRING_DATASOURCE_PASSWORD	Database password used by the Spring Boot app
MYSQL_ROOT_PASSWORD	Root password for the MySQL container
MYSQL_DATABASE	Name of the initial MySQL database to be created

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🧠 Design Decisions

• Multi-stage build: Keeps final image small by discarding Maven and source code.
• Isolated network: Ensures secure inter-service communication.
• Healthchecks + depends_on: Guarantees the Java app only starts after MySQL is healthy.
• Named volume for MySQL: Preserves data across container restarts.